Birds do have upper and lower eyelids that can close up to protect their eyes and prevent them from drying out. Many birds also have hair-like feather ,that look just like eyelashes. Unlike humans, however, they have an extra or third eyelid called the ‘nictitating membrane’, which helps keep the eyes clean by removing dust and other things that get into their eyes. The nictitating membrane closes across the eye from its inner corner, moving sideways to the outer corner.

Unlike the main eyelids, the nictitating membrane is semi-transparent so that birds can continue to see while flying or feeding, which could be important in the split seconds that they may have for catching prey or escaping predators. Diving birds, such as cormorants and some ducks, even have small transparent windows in their nictitating membranes so that they can see while swimming underwater.